Which insurance license is the best one to get?
No single license is best; the right one depends on what you plan to sell. The two main paths are life and health, covering policies, annuities, medical, and long-term care insurance, and property and casualty, covering home, auto, commercial, and liability insurance; in Texas, one general lines property and casualty license covers all of those products. To sell variable products such as variable annuities, you need a state life license plus registration with the Financial Industry Regulatory Authority (FINRA), typically the Series 6, 7, or 63 exam.
No license is objectively best; the choice depends on the products you plan to sell. A Life Agent license covers human lives, endowment and annuity benefits, and death or dismemberment by accident; an Accident and Health license covers sickness, bodily injury, and disability income; Property and Casualty covers property and liability lines. You can combine Life and Accident and Health, or Property and Casualty, with one combined exam and one filing fee.
Sources: Cal. Ins. Code Ch. 5 Art. 3: Licensing (1631-1651); Cal. Ins. Code Ch. 5 Art. 7: License qualification examinations (1675-1684).